This invention relates to a device for giving a pattern a rotation which is selected from integral multiples of 90.degree.. A pattern rotating device of this type is useful, for example, in rotating either a scene to be displayed on a cathode-ray tube or a part thereof.
Such a rotation of an original pattern may be carried out by the use of software, as by resorting to a microprocessor with the pattern stored in a memory preliminarily before rotation. In general, the memory must have a large memory capacity. A long processing time is therefore necessary on carrying out the rotation by software. For instance, the memory capacity must be about four megabits when a black and white pattern of the size of ISO A4 is stored in the memory with a resolution of eight lines per millimeter. Under the circumstances, it takes more than one minute of time when an eight-bit microprocessor is put into operation with a sequence of reference clocks of 4 MHz.
A hardware device is revealed in Japanese Patent Publication No. Syo 56-18989 published May 2, 1981. As will later be described in conjunction with an embodiment of the present invention with reference to one of twelve figures of the accompanying drawing, a predetermined number of unit shift registers are used according to the patent publication. An original pattern to be rotated, is read into the shift registers. A rotated pattern is obtained by reading the shift registers in a predetermined order. The patent publication merely teaches a numeral as the "pattern." The numeral is represented by, for example, a matrix of seven by five dots or picture elements. In this event, the shift registers may be seven in number.